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Altres ajuts: Institució Catalana de Recerca i Estudis Avançats This article presents a low-cost and portable phase-variation planar microwave sensor operating in reflective mode, where the output variable, the phase of the reflection coefficient of the one-port sensing element, is retrieved by means of a distributed circuit based on a pair of rat-race hybrid couplers and the associated electronics. This includes a microcontroller, a voltage controlled oscillator (VCO), a digital-to-analog converter (DAC), and an RF/microwave gain/phase detector. By this means, vector network analyzers (VNAs), i.e., high-cost instruments typically used for obtaining the reflection coefficient in one-port structures or circulators (microwave components able to separate the injected signal from the reflected signal in any one-port network) are avoided. Indeed, the presented architecture (including the microwave rat-race hybrid configuration and the associated electronics) can be adapted to other one-port reflective-mode phase-variation microwave sensors. A prototype example, where the sensing element is a one-port step-impedance open-ended transmission line, is reported. The device provides the phase of the reflection coefficient of the sensing element as a function of the dielectric constant of the material under test (MUT) with a maximum sensitivity of −65.7° and a relative error of less than 8% in all the measurements.

Altres ajuts: Secreteraria d'Universitats i Recerca (Generalitat de Catatunya), European Social Fund for the FI Grant, Institució Catalana de Recerca i Estudis Avançats This paper presents a single-frequency reflective-mode phase-variation microwave sensor devoted to the dielectric characterization of materials. The device is implemented in coplanar waveguide (CPW) technology and consists of two parts: (i) the sensing region, a step-impedance resonator (SIR) as termination of a CPW transmission line, and (ii) the design region, a cascade of high/low impedance quarter-wavelength inverters, used to boost up the sensitivity. By placing the so-called material under test (MUT) on top of the sensing region, the capacitance of the SIR is altered due to the effects of the dielectric constant of the MUT. This modifies the phase of the reflection coefficient seen from the input port, the output variable. From a circuit analysis, it is demonstrated that the sensitivity for small perturbations in the vicinity of the dielectric constant of a reference (REF) material can be optimized by setting the operation frequency of the sensor to the resonance frequency of the SIR loaded with such REF material. The maximum sensitivity in one of the reported sensors is as high as 66.5°, and the main figure of merit, defined as the ratio between the maximum sensitivity and the area of the sensing region expressed in terms of the squared guided wavelength, is FoM=3643∘/λ2 . Such figure of merit represents a significant improvement as compared to the one of the equivalent sensor implemented by means of an open-ended quarter-wavelength sensing line. Such equivalence between the semi-lumped element (i.e., SIR-based) sensor and the fully distributed counterpart is also analyzed in the paper.

This paper presents an active microwave sensor for the characterization of dielectric materials. The sensor is consisted of a microstrip complementary split-ring resonator (MCSRR) structure and an active feedback loop. The loop uses an amplifier to generate negative resistance to compensate the resonator’s loss and increase the loaded quality factor. The developed sensor possesses the advantages of high quality factor, ultra-small electrical size, and high sensitivity. A prototype of the sensor is fabricated and measured for validation.

None-invasive blood glucose measurement enables effective diagnosis and treatment of diabetic patients. The existing microwave sensors suffer from low sensitivity and large size. This article presents a highly sensitive and compact size non-invasive microwave sensor for real-time blood glucose measurements. We have developed a new sensing technique using directly connected Branch Line Coupler and Split Ring Resonators. This technique significantly improves the sensitivity by mitigating the limited coupling between transmission lines and resonators. In addition, using Split Ring Resonators reduces the sensor size due to capacitive and inductive effects, which are loaded to the Branch Line Coupler. The proposed sensing function is based on shifting the transmission notch frequency in coupled arm of the Branch Line Coupler, which is caused by loading the Split Ring Resonators with varying glucose concentration. A prototype sensor is fabricated and successfully tested using several glucose concentrations in deionized water. Experimental results demonstrate 0.72 MHz/mgdL−1 measurement sensitivity, which is higher in comparison with available sensors in PCB technology. The prototype sensor size is $3.5\times 3.5\times 0.16$ cm3.

In daily life, people consume many liquids in their diet like water, soda, milk, juices, etc. Due to the growing demand of these liquids, many adulterants are being used in the market, which degrades the quality of the product and may be harmful to the human being’s health. For a human being, it is very difficult task to find out adulteration in the liquids that they are having in their daily diet. In order to resolve this problem, a device that is very easy to use and provides quick and accurate results is designed, where change in resonant frequency is the parameter used for adulteration detection. In this paper, a split ring resonator-based microwave sensor is proposed for the detection of adulteration in different fluids. The resonant frequency of the sensor is 9.24 GHz. The sensor design exhibit defected ground structure to obtain a sharp resonant frequency. The proposed sensor is fabricated and tested by using water and milk with adulteration (sugar, salt and soap). 2 µl drop of each fluid is placed on the sensor and a shift in resonant frequency from 9.24 to 7.3 GHz for water and 8.4 GHz for milk is noticed.

One of the most important characteristics of planar microwave resonator-based sensors is their sensitivity. Since their measuring parameter is resonance frequency shift, the sensitivity could be described as the shift in the resonance frequency of the microwave resonators versus variation in the dielectric constant of the material under the test. Although label-free microwave resonator-based sensors are capable of providing moderate levels of sensitivity sufficient for enabling numerous applications, detection of material variations in sub-percent or ppm (part per million) range is not easily possible with these structures. This paper investigates the reasons behind the limited sensitivity of planar microwave resonator-based sensors and suggests a measurement structure capable of measuring extremely low concentrations of water contamination in mineral oil samples. Simulation and experimental results verify the capability of the presented sensing structure in the detection of as low water concentrations as 50 ppm in mineral oil samples expressing extremely high sensitivity for the presented sensor with 30 kHz in the frequency shift of the resonator.

Water pollution and scarcity of pure drinking water is a current challenging problem. In this situation, quality monitoring of water is of vital importance in order to avoid any health issues caused due to intake of contaminated water. Hence, in this paper, a non-destructive technique using multiple ring CSRR based microwave sensor has been proposed for accurate estimation of relative permittivity of unknown water of varying TDS values. Further, a closed form numerical expression using the curve fitting technique has been developed in order to accurately estimate the quality of any unknown water sample. Less than 1% of error has been achieved in the prediction of relative permittivity and hence, TDS of unknown water sample. The proposed planar microwave sensor will be of great importance towards the real-time water quality monitoring systems development.

This study estimates the random error variances and standard deviations (STDs) for four datasets: Global Hawk (GH) dropsondes (DROP), the High-Altitude Monolithic Microwave Integrated Circuit Sounding Radiometer (HAMSR) aboard the GH, the fifth European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5), and the Hurricane Weather Research and Forecasting (HWRF) Model, using the three-cornered hat (3CH) method. These estimates are made during the 2016 Sensing Hazards with Operational Unmanned Technology (SHOUT) season in the environment of four tropical cyclones from August to October. For temperature and specific and relative humidity, the ERA5, HWRF, and DROP datasets all have similar magnitudes of errors, with ERA5 having the smallest. The error STDs of temperature and specific humidity are less than 0.8 K and 1.0 g kg−1 over most of the troposphere, while relative humidity error STDs increase from less than 5% near the surface to between 10% and 20% in the upper troposphere. The HAMSR bias-corrected data have larger errors, with estimated error STDs of temperature and specific humidity in the lower troposphere between 1.5 and 2.0 K and between 1.5 and 2.5 g kg−1. HAMSR’s relative humidity error STD increases from approximately 10% in the lower troposphere to 30% in the upper troposphere. The 3CH method error estimates are generally consistent with prior independent estimates of errors and uncertainties for the HAMSR and dropsonde datasets, although they are somewhat larger, likely due to the inclusion of representativeness errors (differences associated with different spatial and temporal scales represented by the data).

This article presents a microwave sensor composed of a cylindrical cavity resonator and thin plastic liquid container for noncontactual detection of the liquid solution concentration. The resonant frequency is tuned to around 11 GHz, resulting in miniaturized dimensions and easy integration with a wireless sensor system. The sensor is with a small volume of 21 cm3 and sensitivity of 0.4 kHz/(mg/L). Simulated results show a good linear relationship between the concentration of the sample solution and resonant frequency shift with the high sensitivity, which is consistent with the experimental result. Compared with other designs, the sensor also has a simple structure, low cost and easy implementation to in-situ and in-vitro detection scenarios.

In this work, a compact, inexpensive, and efficient dual band microwave sensor is proposed. The sensor is based on two Complementary Symmetric Split-Ring Resonators (CSSRRs) and possesses a high $Q$ factor and wide sensing range. These CSSRRs are coupled electrically with two inductive patches to the Microstrip Transmission Line (MTL). This combination provides two dual bands, first at 5.35 GHz with a notch depth of -55.20 dB and second at 7.99 GHz with a notch depth of -22.54 dB. The sensor works in transmission mode and senses shift in frequency. Some commonly available dielectric substrates with relative permittivity ranges between 1 and 12 are considered Material Under Test (MUT), and detailed sensitivity analysis is being performed for each band. The dual band sensor is fabricated on a low-cost, widely available FR4 substrate and measured by CEYEAR AV3672D vector network analyzer. Additionally, the least square curve fitting method is used to develop a mathematical model for the measured results. An excellent agreement is observed between simulated, measured, and formulated results.

A novel sensing method that uses the separate design of a sensitivity enhancer and sensing zone is reported. Unlike most resonance-based sensors, the flexible design of a sensing zone is beneficial to the increment of effective material-under-test volume. A novel technique to enhance sensitivity is proposed by engineering the −1/ $x$ -like function microwave transmission to slow the energy-flow velocity. The measured large group delay is up to $\sim 16~\mu \text{s}$ at 2.967 GHz. A lumped model is built to study the condition of the engineered transmission. Compared with a regular coplanar waveguide sensor, the sensitivity is improved up to ~227 times when it is connected to the slow microwave circuit.

The jugular venous pulse (JVP) waveform provides an insight into right heart function, and its assessment is important in patients with heart failure. However, the conventional pulse-transducer (contact) method for monitoring this waveform is not frequently used because it requires a high degree of skill. The aim of this study was to confirm the effectiveness of a prototype non-contact system that employs microwave radar (24 GHz, 7 mW; non-contact system) for JVP measurement. Experiments were conducted on eight healthy male volunteers (21.88 ± 0.99 years). JVP measurements were compared between the conventional contact method and the proposed non-contact method. Change in JVP waveform was measured in response to an angle of reclining in five steps from the supine position to 75° of elevation. The obtained JVP measurements were similar between the two methods. Because in the non-contact method the faint pulsation of the JVP is not suppressed by the pressure of a sensor placed on the skin, the prototype microwave radar system is particularly suitable for evaluating the JVP waveform.

Altres ajuts: Universidad Politécnica de Madrid Young Researchers (Grant Number: VJIDOCUPM18MGB) i ICREA This article presents an exhaustive study of the sensitivity in reflective-mode phase-variation sensors based on an open-ended transmission line with a step-impedance discontinuity. Such discontinuity delimits the sensing region (which extends up to the open end of the so-called sensing line), from the transmission line section connected to the input port (design line), which is used to enhance the sensitivity. The theoretical analysis provides the design guidelines to achieve a sensor with high sensitivity compared with the one based on an ordinary (uniform) line with a similar length. In particular, it is shown that for sensitivity optimization, the electrical length of the design line must be set to 90° (or an odd multiple), whereas either a 90° (or an odd multiple) or a 180° (or an even or odd multiple) sensing line can be alternatively used in order to maximize the sensitivity. It is shown that the impedance contrast, defined as the ratio between the characteristic impedances of the design and sensing line, is a key parameter for sensitivity enhancement, and it must be as low or as high as possible for the 90° or 180° sensing lines, respectively. For validation purposes, two prototype devices (one with a 90° and the other one with a 180° sensing line) have been designed and fabricated following the design guidelines. Such devices have been tested by loading the sensing region with several materials with different dielectric constants. Compared with the ordinary line-based sensors, it is found that the maximum sensitivity is enhanced by a factor of 19.7 and 11.4 in the phase-variation sensor based on a 90° and 180° sensing line, respectively. Finally, the sensor concept is generalized to a multisection step-impedance transmission line as a means of further increasing the sensitivity, and a prototype device exhibiting 528.7° maximum sensitivity is implemented.

Ship detection by an airborne passive interferometric microwave sensor has been proposed as a powerful complementary tool for ship detection, especially for large ships in low visibility conditions and high sea clutter. In this article, the brightness temperature (TB) models of the sea background and the ship on the sea are established. Given the TB models, a ship detection and tracking algorithm with four steps is proposed, which is devoted to ship tracking. In addition, the impacts of the noises in the passive interferometric microwave images (PIMI) and the algorithm parameters are analyzed and discussed. Numerical simulations and airborne experiments are performed to assess the practicability of the algorithm. Both numerical and experimental results have demonstrated the practicability of the proposed algorithm with dealing with the additional systematic errors and estimating the ship heading, and the results also exhibit that the additional noises in the PIMI caused by the stochastic fluctuations of the aircraft and the algorithm parameters have a non-negligible impact on the algorithm detection performance. As a result, the “ship-free” observed TB maps should be carefully considered as the sea background TB map to improve the algorithm detection performance by reducing the noises caused by the stochastic fluctuations of the aircraft. In addition, the algorithm parameter should also be carefully considered to get a high ship detection probability with a low ship false-alarm rate.

A planar sensor designed using the fourth Hilbert fractal curve iteration for solid material characterization at multiple frequencies is reported in this paper. The fractal curve is self-similar with space filling properties. The Hilbert fractal geometry is used to form a compact resonator, with a multiband frequency response where miniaturization is achieved, since a large transmission line length is effectively confined in a limited area. The sensor provides five resonances in the frequency range from 0 to 5 GHz. The resonant frequencies are 0.56, 1.68, 2.72, 3.69 and 4.72 GHz, all used to measure the real permittivity of known samples with a sensitivity of 7, 20, 27, 43 and 50 MHz/permittivity, respectively. The sensor is used to measure dielectric samples with 20 x 20 mm2 areas with several thicknesses. Simulations and measurements demonstrate that the Hilbert fractal geometry can be used to design a multiband planar sensor for solid dielectric material characterization.

In this study, a loss-compensated microwave (MW) planar sensor is used to characterize fluids at ~1 GHz. The environmental temperature is shown to adversely impact the recorded resonance frequency of the MW sensor, leading to data mixing. This issue is resolved using a feedforward artificial neural network with two hidden layers. Various concentrations of methanol in water (0%-100% with 10% increments) are measured at temperatures ranging between 22 °C and 60 °C. This smart sensor system exhibits a strong ability to discriminate the correct data regardless of erroneous interfering factors up to 92%.

An angular displacement sensor is designed using a corrugated substrate integrated waveguide (CSIW) cavity resonator. Where, in the proposed cavity, instead of copper vias, one of the electric wall...

Resonant coaxial SMA microwave permittivity sensor is introduced. It is constructed using only commercially available SMA connectors. The sensor is tested in two different frequency ranges for two different dielectric constant ranges, from 1 to 10 and from 10 to 80. Presented sensor is designed, fabricated, simulated, and tested. Good agreement between simulations and measurements is shown. The sensor is also applicable for differential permittivity measurements.

In this study, a portable prototype of a planar microwave sensor is proposed for intermittent glucose level monitoring. The sensor element basically consists of four distinct hexagonal-shaped complementary split ring resonators (CSRRs) configured in the honey-cell pattern and fabricated on an FR4 dielectric substrate. The CSRRs are coupled via microstrip transmission line to a radar system operating in the ISM band 2.4–2.5 GHz. The integrated sensor shows a remarkable detection sensitivity for the diabetes-spectrum glucose levels dissolved in the blood mimicking aqueous solutions. This is demonstrated by the raw data collected by the radar receiving channel, which shows a clear trend following the variations in glucose levels.

A microwave device able to detect differential-mode to common-mode conversion (or vice versa) in a four-port balanced circuit is proposed. For mode conversion detection, the balanced circuit should be fed by a differential-mode signal, generated by means of a rat-race balun from a single-ended signal. By connecting the pair of output ports of the balanced circuit under test to one of the two pairs of isolated ports of a second rat-race coupler, conversion to the common-mode (if it exists) can be detected and recorded in the $\Sigma $ -port. Since the signal level at the output (single-ended) port depends on mode conversion efficiency, the complete two-port structure, including the pair of rat-race couplers plus the balanced circuit in between, can be used as a comparator or differential microwave sensor based on mode conversion. In such a sensor, the working principle is symmetry disruption (caused, e.g., by an asymmetric dielectric load), and the output variable is the transmission coefficient, related to the level of asymmetry. A detailed analysis, considering an arbitrary unbalanced four-port test structure (to account for symmetry disruption), is carried out. Then, such analysis is particularized to the case of a pair of unbalanced and uncoupled matched lines, and the conditions for sensitivity optimization are obtained. Finally, a differential sensor and comparator based on a pair of balanced (and meandered) matched lines, designed according to the guidelines for sensitivity optimization, is fabricated and validated.

The aqueous solution with iron nanoparticles investigated by a microwave stripline sensor based on the optimized double quadratic-shape design. Due to real-time near-field electromagnetic interaction between microwaves and sample S11 reflection coefficient of the sensor was changed depending on iron nanoparticles concentration in the aqueous solution at resonant frequencies. In this work we examined the iron nanoparticles concentration in the 0–20 µg/L concentration range at an operating frequency of about 1.7 GHz. The measured minimum detectable signal was 0.035 dB/(µg/L) and 0.25 MHz/(µg/L) and the measured minimum detectable concentration was 1.4 µg/L and 0.2 µg/L, respectively. The microwave response of sensor systems can be explained by the additional structural changes of water clusters due to the metal nanoparticles ablation. This implemented method has approachable development process and the accuracy of measurement is high, thus it can be applied as a physiochemical sensor for non-invasive monitoring of metal nanoparticles in complex liquids.

Ship detection is important for a wide range of applications. In this article, an airborne passive interferometric microwave sensor (PIMS) is proposed as a powerful complementary tool for ship detection. The fundamental of ship detection by the airborne PIMS is introduced. A specification called “the detection factor” is addressed to quantitatively assess the performance of the airborne PIMS for ship detection. The detection probability is discussed and addressed based on the constant false-alarm rate (CFAR). Numerical simulations are performed to demonstrate the feasibility of ship detection by the airborne PIMS. The impacts of the atmosphere and the sea wind on the performance of the airborne PIMS for ship detection are also addressed in terms of theoretical analyses and numerical simulations. The airborne experiments are also carried out by an X-band PIMS to verify the practicability of ship detection by the airborne PIMS in a sunny weather and a cloudy weather. The data processing procedure and a ship detection algorithm in the experiments are introduced. The airborne experimental results reveal that the ships can be effectively detected and tracked by the airborne X-band PIMS in a sunny weather and a cloudy weather. It demonstrates the practicability of ship detection by the airborne PIMS. The ship detection probability is also analyzed, which agrees well with the theoretical detection probability.

This study involved the creation and assessment of a microwave sensor to measure glucose levels in aqueous solutions without invasiveness. The sensor design utilized a planar interdigital capacitor (IDC) loaded with a hexagonal complementary split-ring resonator (HCSRR). The HCSRR was chosen for its ability to generate a highly intense electric field that is capable of detecting variations in the dielectric characteristics of the specimen. A chamber tube was used to fill glucose solutions at the sensor’s sensitive area, and changes in the device’s resonance frequency (Fr) and reflection coefficient (S11) were used to measure glucose levels. Fitting formulas were developed to analyze the data, and laboratory tests showed that the sensor could accurately measure glucose levels within a range of 0–150 mg/dL. At a concentration of 37.5 mg/dL, the sensitivity based on S11 and Fr reached maximum values of 10.023 dB per mg/dL and 1.73 MHz per mg/dL, respectively. This implies that the sensor put forward has the possibility of being utilized in medical settings for the monitoring of glucose levels.

Microwave electromagnetic devices have been used for many applications in tropospheric communication, navigation, radar systems, and measurement. The development of the signal preprocessing units including frequency-selective devices (bandpass filters) determines the reliability and usability of such systems. In wireless sensor network nodes, filters with microstrip resonators are widely used to improve the out-of-band suppression and frequency selectivity. Filters based on multimode microstrip resonators have an order that determines their frequency-selective properties, which is a multiple of the number of resonators. That enables us to reduce the size of systems without deteriorating their selective properties. Various microstrip multimode resonator topologies can be used for both filters and microwave sensors, however, the quality criteria for them may differ. The development of every resonator topology is time consuming. We propose a technique for the automatic generation of the resonator topology with required frequency characteristics based on the use of evolutionary algorithms. The topology is encoded into a set of real valued parameters, which are varied to achieve the desired features. The differential evolution algorithm and the genetic algorithm with simulated binary crossover and polynomial mutation are applied to solve the formulated problem using the dynamic penalties method. The experimental results show that our technique enables us to find microstrip resonator topologies with desired amplitude-frequency characteristics automatically, and manufactured devices demonstrate characteristics very close to the results of the algorithm. The proposed algorithmic approach may be used for automatically exploring the new perspective topologies of resonators used in microwave filters, radar antennas or sensors, in accordance with the defined criteria and constraints.

An automatic humidity control system for mushroom growing house based on the free-space technique is presented. The novelty of this work is the modified free-space technique by measuring the amplitude only of transmission coefficient |S21| that reflected from mushroom by using beam-switching antenna with artificial neural networks (ANNs) as a humidity sensor to control quantity and time of water misting nozzle. In the proposed system, the antenna is designed to act as the transmitting antenna at the frequency of 2.45 GHz. Its radiation patterns can be switched to 4 directions covering all corners of mushroom growing house. The measured |S21| from each direction are converted to direct current (DC) voltage by a radio frequency (RF) detector; then are trained with ANNs in the humidity range of 60-85%. The optimized ANNs structure consists of 4 input nodes, two layers of 5 hidden nodes, and 3 output nodes. To verify the proposed system, experiments were set up in controlled humidity mushroom growing house at the humidity level of 75-80% for 120 hours. The results showed that there was slightly average standard deviation (S.D.) of humidity level 1.36. Consequently, the performance of sensor system assures that it is able to apply for humidity control in large growing house.

This paper presents the design, optimization, and calibration of multivariable resonators for microwave dielectric sensors. An optimization technique for the circular complementary split ring resonator (CC-SRR) and square complementary split ring resonator (SC-SRR) is presented to achieve the required transmission response in a precise manner. The optimized resonators are manufactured using a standard photolithographic technique and measured for fabrication tolerance. The fabricated sensor is presented for the high-resolution characterization of dielectric substrates and oil samples. A three-dimensional dielectric container is attached to the sensor and acts as a pool for the sample under test (SUT). In the presented technique, the dielectric substrates and oil samples can interact directly with the electromagnetic (EM) field emitted from the resonator. For the sake of sensor calibration, a relation between the relative permittivity of the dielectric samples and the resonant frequency of the sensor is established in the form of an inverse regression model. Comparisons with state-of-the-art sensors indicate the superiority of the presented design in terms of oil characterization reliability. The significant technical contributions of this work include the employment of the rigorous optimization of geometry parameters of the sensor, leading to its superior performance, and the development and application of the inverse-model-based calibration procedure.

In this paper, a new non-contact method for detection of impact damage in carbon fibre-reinforced polymer composites with a complementary split-ring resonator sensor is proposed. The resonance frequency is evaluated as an indicator of the presence of damage. The resonator is made on a printed circuit board, and in the experimental setup it is positioned close to the area of interest. Electromagnetic models are built, and from the resonant responses the appropriate frequency range used for the test is determined. The active sensing element in the resonator is found from the analysis of the magnetic field distribution. The parametric study performed shows that a larger frequency change occurs for a wider impacted region, which is of great use for practical applications. The proposed method is validated by the experimental results, where a frequency shift of 65 MHz was observed for a 0.36 mm deep dent.

In this study we present a microwave sensor based on the quadratic-shape and designed for detecting glucose concentration in aqueous solutions by using a microwave near-field electromagnetic interaction technique. We found a linear relationship between the microwave $ S_{11} $ reflection coefficient of the suggested system and the concentration of glucose in solution. Due to this linear relationship we were able to determine the glucose concentration in the range of 0–250 mg/dL at an operating frequency near 3.6 GHz. The measured minimum detectable signal was 0.0044 dB/(mg/dL) and the measured minimum detectable concentration was 6.8 mg/dL. These results suggest that the system we offer has a high enough accuracy for non-contact glucose monitoring and provides a promising basis for developing a non-invasive glucometer.

The research of chiral materials in microwaves is attractive in a lot of physical disciplines. Compared to the field of optics, where many theoretical and measurements analysis tools and techniques exist, in microwaves, the study is at its initial stages of development. Recently, microwave devices based on a ferrite disk resonator with magneto-dipolar-mode (MDM) oscillations that allow creation of near fields characterized by helical structure have been developed. These near fields, called magneto-electric (ME) fields, are essential for the chirality characterization of the sample. For effective focusing of the ME fields a special microwave device based on a metallic wire positioned above a ferrite disk was developed. Such a device allows to narrow down the effective area of the ME fields by more than an order. In this work, we show a theoretical analysis of the localized ME fields generated by a metallic wire on a ferrite disk operating as the microwave microscope. Realization of such localized ME fields is an important step in the development of a microwave sensor for effective sensing of natural and artificial enantiomeric materials.

A conventional cavity-based planar cylindrical resonant sensor for the RF characterization of dielectric materials is proposed in this work. The designed planar cylindrical sensor is about ...

Synthetic aperture radar (SAR) is an active imaging microwave sensor. Since SAR imaging is robust against weather, light, and other external conditions, Ship Detection based on SAR Imaging has high research and application values. However, the variety in size, direction, background and arrangement poses great challenges to SAR image ship detection. Due to the lack of effective constrains, plenty of boxes predicted by the existing methods are quite different from groundtruth, resulting in IOU between predicted boxes and groundtruth being smaller than the threshold and generates false alarms. Therefore, in this letter we propose a method of noisy ship direction classification, which uses the ship pixel distribution in SAR images to classify ship objects into different directions, so as to reduce the shape difference between boxes and groundtruth. Experimental results show that by combining with YOLOv5 framework, our method can significantly improve the ship's detection performance, and reach state-of-the-art.

A microwave metamaterial-inspired sensor based on a 13×13 arrays of Asymmetric Electric Split-Ring Resonator (AESRR) is proposed for dielectric characterization of organic liquids and solid dielectric substrates with low permittivity. The sensor, excited by a pair of patch antennas and working at around 11.575 GHz, is fabricated using printed circuit board (PCB) technology. T-shape channel was integrated to the sensor by grooving in the FR-4 substrate which improved the integration and provided the feasibility of liquids detection. Seven liquids and four dielectric substrates are measured by this sensor. The measured results show the transmission frequency shifts from 11.575 GHz to 11.150 GHz as the liquid samples permittivity changes from 1 to 7 and the transmission frequency shifts from 11.575 GHz to 8.260 GHz as the solid substrates permittivity changes from 1 to 9. The measured results have proven the improved sensitivity and the larger frequency shift ∆f on material under test (MUTs) compared with the conventional reported sensor. The relative permittivity of liquid samples and solid samples can be fitted by establishing approximate models in CST, respectively. Two transcendental equations derived from measured results are proposed to predict the relative permittivity of liquid samples and solids samples. The accuracy and reliability of measured results and predicted results are numerically verified by comparing them with literature values. The proposed sensor has many advantages, such as low-cost, high-sensitivity, high-robustness, and extensive detecting range, which provided a great potential to be implemented in a lab-on-a-chip sensor system in the future.

The recent years have seen a surge in interest in determining the dielectric constant of biological tissues in the microwave domain. The tissues can be classified and differentiated without radiation by using a microwave sensor. The atherosclerotic plaque of the carotid artery, which is now predominantly classified by ultrasonography and the CT scanner was not studied yet. Ultrasonography describes the level of echogenicity of the plaques, and proposes that as a representation of the plaque's composition. In this study, a microwave subwavelength resonator was employed to measure 20 carotid artery plaques and compare the results with ultrasound b-mode images. The results of the study show a correlation between the echogenicity levels and the dielectric constant of the tissues investigated. The way in which it will be evaluated in the future is how it compares to other radiological techniques.

In this paper, the design of a novel multi-resonance microwave resonance sensor for moisture monitoring of pharmaceutical granulations is reviewed. This sensor allows a reliable determination of residual moisture directly in the production container. The reliably determinable measuring range could be extended from below 10% to at least 20% independent of other physical attributes and thus covers the complete moisture range typically occurring in fluid bed granulations. For this purpose, experimental prototypes with a novel electronic structure were developed. In order to enable the installation in the various granulators, prototypes with different dimensions of the sensor heads were realized. Within this publication, the measurement principle will be reviewed and prospects for the multi-resonance sensor will be provided.

A complex permittivity characterization method for liquid samples has been proposed. The measurement is carried out based on a self-designed microwave sensor with a split ring resonator (SRR), the unload resonant frequency of which is 5.05 GHz. The liquid samples in capillary are placed in the resonant zone of the fabricated senor for high sensitivity measurement. The frequency shift of 58.7 MHz is achieved when the capillary is filled with ethanol, corresponding a sensitivity of 97.46 MHz/μL. The complex permittivity of methanol, ethanol, isopropanol (IPA) and deionized water at the resonant frequency are measured and calibrated by the first order Debye model. Then, the complex permittivity of different concentrations of aqueous solutions of these materials are measured by using the calibrated sensor system. The results show that the proposed sensor has high sensitivity and accuracy in measuring the complex permittivity of liquid samples with volumes as small as 0.13 μL. It provides a useful reference for the complex permittivity characterization of small amount of liquid chemical samples. In addition, the characterization of an important biological sample (inositol) is carried out by using the proposed sensor.

In this preliminary study, we investigate how changes in breast tissue due to treatment can be quantified using microwave signals, images, and property estimates. Microwave scans of treated and healthy breasts from a group of cancer patients before and after radiation treatment are compared. Images of the treated breasts generally had an increase in permittivity after treatment, while the healthy breast remained relatively constant over the timeframe. In a case study, the permittivity estimated at various microwave sensor pairs was generally higher for the treated breast compared to the healthy breast, however changes were small in the reported patient. For this example, the signal correlation between scans was high and similar for both the treated and the healthy scan. For the same patient, image correlation highlighted differences between the baseline and follow-up scans, suggesting that image correlation may be a better metric for quantifying changes.

Microwave sensors are principally sensitive to effective permittivity, and hence not selective to a specific material under test (MUT). In this work, a highly compact microwave planar sensor based on zeroth-order resonance is designed to operate at three distant frequencies of 3.5, 4.3, and 5 GHz, with the size of only λg−min/8 per resonator. This resonator is deployed to characterize liquid mixtures with one desired MUT (here water) combined with an interfering material (e.g., methanol, ethanol, or acetone) with various concentrations (0%:10%:100%). To achieve a sensor with selectivity to water, a convolutional neural network (CNN) is used to recognize different concentrations of water regardless of the host medium. To obtain a high accuracy of this classification, Style-GAN is utilized to generate a reliable sensor response for concentrations between water and the host medium (methanol, ethanol, and acetone). A high accuracy of 90.7% is achieved using CNN for selectively discriminating water concentrations.

A microwave sensor is designed to operate at 2.4 GHz for measuring vital signs in human body. A double-layer patterned ground plane (GP) has been conceived to minimize the sensor size and experimentally verified. More than 360 MHz of 10 dB bandwidth and 2.28 dBi of gain over this band makes this sensor suitable for medical application. The simulated SAR value is found to be 0.5 W/kg for 30 mW of input power, which is much less than maximum limit 1.6 W/kg average over 1 g provided by FCC.

A planar sensor designed using the fourth Hilbert fractal curve iteration for solid material characterization at multiple frequencies is reported in this paper. The fractal curve is self-similar with space-filling properties. The Hilbert fractal geometry is used to form a compact resonator, with a multiband frequency response where miniaturization is achieved since a large transmission line length is effectively confined in a limited area. The sensor provides five resonances in the frequency range from 0 to 5 GHz. The resonant frequencies are 0.56, 1.68, 2.72, 3.69 and 4.72 GHz, all used to measure the real permittivity of known samples with a sensitivity of 7, 20, 27, 43 and 50 MHz/permittivity, respectively. The sensor is used to measure dielectric samples with 20 x 20 mm(2) areas with several thicknesses. Simulations and measurements demonstrate that the Hilbert fractal geometry can be used to design a multiband planar sensor for solid dielectric material characterization.